Some countries join interstate wars well after the war has begun, waiting months and often years, and thus changing their beliefs about the wisdom of entering a war. This volume examines why this might be so, focusing on unforeseen events in wars which cause neutral players to update their expectations about the trajectory of the war, therefore explaining why some wars spread while others do not.

The author uses a combination of case studies and statistical analysis to test this theory: the Crimean War, the Franco-Prussian War, World War I, and a study of the spread of war since World War II. Designed for courses on and research into war and other international security issues, this book is a must read.

Contents: The puzzle of why states join ongoing wars; Previous findings and the new theory of joining; Statistical analysis of the spread of war; The Crimean War: public opinion, divided cabinets, and the partial spread of war; The First World War: the growth of a world war; The Franco-Prussian War: the war that refused to grow; Joining since 1945: balancing bandwagoning and the changing nature of spoils; Conclusions, extensions, and avenues for future research; Appendix; Bibliography; Index.

About the Author: Zachary C. Shirkey is an Assistant Professor of Political Science, Hunter College, CUNY, USA

Reviews: 'Existing work shows how interstate conflicts often spread beyond initial disputants, yet we still lack satisfactory answers to why states chose to join ongoing wars or abstain. This insightful book highlights how unexpected events during conflicts influence states’ decisions to join or leave conflicts and provides a useful framework for understanding the dynamics of war and conflict expansion.' Kristian Skrede Gleditsch, University of Essex, UK and International Peace Research Institute, Norway

'Rigoureux dans sa méthodologie, l’ouvrage de Shirkey s’inscrit dans une lignée de travaux consacrés à l’étude quantitative des confl its et des multiples questions s’y rattachant. Mêlant de manière équilibrée quantitatif et qualitatif, l’auteur tente d’apporter une réponse à une interrogation précise qu’il refuse, en bon rationaliste, de laisser au hasard… (Rigorous in its methodology, Shirkey's book belongs to a line of works on the quantitative study of conflicts and the numerous questions linked to them. Combining quantitative and qualitative research in a balanced way, the author attempts to provide an answer to a specific question he refuses, as a good rationalist, to leave to chance…)' Etudes Internationales